Secure NOMA-Aided V2V Communications Over Time-Selective Nakagami-m Fading Channels

This paper examines the secrecy performance of a downlink non-orthogonal multiple access aided vehicular communication system, where a single-antenna legitimate source vehicle transmits its information to two legitimate multi-antenna user vehicles, i.e., far user vehicle and near user vehicle. In addition, there exists a malicious multi-antenna vehicle in the near vicinity that can launch a passive eavesdropping attack. To better describe the vehicular links, we use the first-order auto-regressive process to model nodes' mobility effect and estimate the channel state information using linear minimum mean square error estimation technique. For the considered setup, we derive the exact intercept probability (IP) expressions for both near user and far user vehicles over Nakagami-m fading channels. We then deduce the asymptotic IP expressions for both user vehicles under high average channel gain regime of the legitimate links to obtain further insights into the system's secrecy diversity order. We also discuss the impact of simultaneous improvement in average channel gains of legitimate and wiretap channels on the secrecy diversity performance. Lastly, we employ comprehensive simulations to validate our analytical results and show how the fading severity parameters, nodes' mobility, and imperfect channel estimates affect the IP performance.